DE102007006612A1 - Method for increasing the availability of a global navigation system - Google Patents

Abstract

The invention relates to a method for increasing the availability of a global navigation system, which comprises a plurality of spacecraft (1, 2,..., 11) which respectively transmit information to the terminal (20) for determining the position of a terminal (20). In a first step, information from a plurality of spacecraft (1, 2, ..., 11) is transmitted to the terminal (20). Subsequently, from the plurality of spacecraft (1, 2, ..., 11), a first subset with at least a first spacecraft and a second subset with second spacecraft (1, 2, ..., 11) determined, wherein the second subset of the spacecraft (1, 2, ..., 11) is the difference between the plurality of spacecraft (1, 2, ..., 11) and the first subset of the spacecraft (1, 2, ..., 11) certainly. Furthermore, the integrity risk is determined exclusively from the information transmitted by the second spacecraft (1, 2, ..., 11), whereby the first and the second subset of the spacecraft (1, 2, ..., 11) are determined in such a way the integrity risk, which is ascertained from the information transmitted by the second spacecraft (1, 2,..., 11), compared with the integrity risk resulting from the information of all spacecraft (1, 2,..., 11) of the plurality on spacecraft (1, 2, ..., 11) has been optimized, in particular minimized, is.

Description

The The invention relates to a method for increasing availability a global navigation system, which is several spacecraft includes, for determining the position of a terminal information respectively transmitted to the terminal. The invention further relates to a terminal for determining a position using a global navigation system.

In a global navigation system based on satellites the exact detection of a specified position with respect to the Earth has both a local and a global integrity of a plurality of satellites transmitted to the terminal information. integrity on the one hand means the ability of the global navigation system a user, d. H. the terminal, to warn within a given time if parts of the system for the intended provision should not be used. On the other Page means integrity Likewise, the trust that a user places in reliability the information can be from the navigation system receives. This especially concerns the accuracy of the information.

warnings are necessary, for example, if individual satellite or navigation signals for the Positioning error. Such errors occur, for example then on, when a navigation signal from a satellite to the wrong Time was created (so-called "clock or time correction error ") or was created at a faulty location (so-called "faulty satellite orbit "). These errors can Influence on the actual Have a signal from the satellite to the terminal and can therefore exert a strong influence on the accuracy of navigation.

Around a measurement error in the position determination by the terminal as possible to be small in the well-known global navigation system Galileo the information of all Satellites, of which the terminal Receives information, processed. This approach is based on the assumption that by a maximum number of measurements, each of which from the transmitted to respective satellites Information can be made to be a mistake in the Minimize position determination. An existing constraint is that a maximum of six of the Satellites may be critical satellites. A critical satellite is defined as a satellite whose position information necessary to a integrity risk below a predetermined threshold value (so-called tolerable or allocated integrity risk) to leave. For this reason, the terminal has a function to increase the number of the critical satellite in a terminal geometry. terminal geometry (also: user geometry) means considering those satellites their information for the position determination should be used.

by virtue of the in practice high number of satellites to be considered (at Galileo usually 11) and the given specification of maximum six allowed critical satellites results in practice a disproportionate high non-availability its global navigation system.

It It is therefore an object of the present invention to provide a method for Increase the availability of a specify global navigation system, which is several spacecraft includes, for determining the position of a terminal respectively Transfer information to the terminal. It is a further object of the present invention to provide a terminal for determining a position using a global navigation system specify.

These Tasks are solved by the features of the independent claims. advantageous embodiments find themselves in the dependent Claims.

at a method according to the invention for Increase the availability a global navigation system comprising several spacecraft, for determining the position of a terminal in each case information transmit the terminal, Each of a plurality of spacecraft information transmitted to the terminal. Out The majority of spacecraft will be a first subset with at least a first spacecraft and a second subset of second spacecraft determined. The second subset of spacecraft is determined from the difference between the majority of spacecraft and the first subset of spacecraft. It is made exclusively the information transmitted by the second spacecraft determines an integrity risk, wherein the first and the second subset of the spacecraft such be determined that the integrity risk arising from the, transmitted by the second spacecraft, Information transmitted will, opposite the integrity risk, that from the information of all spacecraft of the majority of spacecraft was determined, is optimized.

One Inventive terminal for determining a position using a global navigation system includes funds through implementation the method according to the invention.

The invention is based on the knowledge that the accuracy for determining the position of the terminal is not dependent on the number of available measurements, which can be undertaken in each case from the information transmitted by the respective spacecraft. Rather, a high accuracy in determining the position can also be determined by a smaller number of measurements. By using a smaller number of spacecraft for a position determination, however, the availability of the navigation system can be increased simultaneously. This is done by optimizing the integrity risk.

The Optimization takes place on the one hand with regard to the shortfall a given tolerable integrity risk and / or on the other hand the number of critical spacecraft, in particular the undershoot a predetermined maximum number of critical spacecraft. The optimization regarding the integrity risk can be achieved and / or the number of critical satellites in that such Spacecraft from consideration for one Positioning be eliminated, their information either in an elevated integrity risk or an elevated one Number of critical spacecraft results. From the majority the spacecraft from which the terminal each receives information are thus in an optimization method spacecraft a first Subset slammed, which does not use for position determination and a second subset, based on their information the position determination should ultimately take place. Only the Information of the second subset of spacecraft for position determination of the terminal used while the information of the first subset of spacecraft not to Position determination of the terminal be used.

According to one embodiment become the first subset and the second subset of spacecraft determined iteratively so that the integrity risk arising from the transmitted from the second spacecraft Information against the integrity risk, that from the information of all spacecraft of the majority of spacecraft was determined is minimized.

to Minimizing the integrity risk becomes a number of spacecraft of the plurality of spacecraft assigned to the first subset and the integrity risk of the second Subset determined remaining second spacecraft. This Step becomes, especially all, possible Combinations of a first subset repeated. The number of spacecraft can in principle be chosen arbitrarily become. Is appropriate it, the iteration first with the number "1." Should If there is no significant reduction in the integrity risk, it can the iteration for example a number of "2" be repeated. This procedure can be extended as desired. Those second Spacecraft of the second subset, where the integrity risk is minimal, make up for a next one Iteration step the majority of spacecraft. The above Steps are repeated until a minimum integrity risk is reached. By the mentioned method steps are successively those spacecraft from a measurement to determine the position of the terminal excluded, which is the largest reduction integrity risk contribute.

there is checked in a further embodiment, whether the Integrity risk, this is due to the successive removal of at least one spacecraft is less than a tolerable integrity risk. Is this the Case, so is the availability of the Navigation system given.

According to one another embodiment is for each of the second spacecraft of the second subset verifies that this a critical spacecraft is. It is a check provided that the number on critical spacecraft greater than is a number of allowed critical spacecraft. Is this the case, so will according to a Another embodiment of the invention attempts to reduce the number of critical Reduce satellites to a tolerable number.

to Minimizing the number of critical spacecraft will be uncritical Spacecraft from the determined, in particular optimal, second Subset of spacecraft assigned to the first subset. This means the uncritical spacecraft is initially excluded from the measurements. Then the number of critical spacecraft within the remaining second subset determined. These steps will be repeated iteratively until in the second subset no uncritical Spacecraft are more determinable. This procedure is the consideration underlying that by further removing a non-critical spacecraft The number of critical spacecraft can also change positively. Can not uncritical spacecraft from the second subset more be removed and after checking the number of critical Subset is below the specified number of critical spacecraft not reached, then the optimization comes to an end here.

The Minimization of the number of critical spacecraft is expediently carried out, if the number of critical spacecraft is greater than a maximum allowed Number of critical spacecraft is.

From The invention further comprises a computer program product which loaded directly into the internal memory of a digital computer can be and includes software code sections that complete the steps of the method according to the invention are carried out, if the product is running on a computer.

The Invention will be explained in more detail with reference to FIGS. Show it:

1 a schematic representation of a global navigation system with example eleven spacecraft, which each transmit information to a terminal to determine its position;

2 to 10 in each case a state of the global navigation system in carrying out the method according to the invention, and

11 an exemplary flowchart of the method according to the invention.

1 shows a global navigation system with exemplarily eleven spacecrafts 1 . 2 , ..., 11 , which each information to a terminal 20 transfer. The terminal 20 is able to get out of the spacecraft 1 . 2 , ..., 11 transmitted information to perform a position determination. The spacecraft are referred to below as satellites.

According to the method of the invention on which the position determination is not the information of all of the available in principle satellite 1 . 2 , ..., 11 but a number of satellites optimized in terms of integrity risk and one of the number of critical satellites. To do this, we will first try to find those satellites whose removal will improve the integrity risk. First of all, the integrity risk is determined from the information of all satellites 1 . 2 , ..., 11 is determined.

Satellites whose information is not used to determine the position of the terminal in the further course 20 are used, are assigned to a first subset. Satellites, which are used for positioning, are assigned to a second subset of satellites. Satellites of the first subset are described below 2 to 5 shown with a broken line. Satellites associated with the second subset, however, are indicated by a solid line.

In a first step, a satellite is first added to the total number of eleven satellites of the first subset. In the presentation of the 2 is doing this with the satellite 1 began. It becomes the integrity risk for the satellites associated with the second subset 2 , ..., 11 determined. It checks to what extent the integrity risk by removing the satellite 1 versus the integrity risk that applies to the entirety of the majority of satellites 1 . 2 , .., 11 was determined, is reduced.

This procedure is repeated in a corresponding manner, according to 3 satellite 2 added to the first subset. Here, the integrity risk for the ten, remaining in the second subset satellites 1 . 3 . 4 , ..., 11 determined. This process is done in a similar way for the satellites 3 . 4 . 5 . 6 . 7 . 8th . 9 . 10 and 11 this repeated in the 4 and 5 exemplary for the satellites 10 and 11 is shown.

The first step involved determining the integrity risk for removing one satellite of all possible eleven combinations. It is assumed in the example that by removing the satellite 2 the integrity risk was reduced the most. satellite 2 will be permanently removed from the majority of the eleven satellites for further consideration. This is through the passage of the satellite 2 symbolizes. satellite 2 is added to the first subset, while the second subset by the satellites 1 . 3 . 4 . 5 . 6 . 7 . 8th . 9 . 10 and 11 is formed. This is schematically in 6 shown.

In a second iteration step forms the according 6 illustrated second subset of the plurality of satellites. This means it will be for the remaining ten satellites 1 . 3 . 4 . 5 . 6 . 7 . 8th . 9 . 10 and 11 the same procedure as in the 2 to 5 described, repeated. It is found, for example, that the further removal of the satellite 10 maximize the integrity risk. satellite 10 is therefore added to the first subset. This is through the passage of the satellite 10 symbolizes. The satellites remain in the second subset 1 . 3 . 4 . 5 . 6 . 7 . 8th . 9 and 11 ,

In a third iteration loop, the described procedure is repeated again. In the embodiment it is assumed that by removing the satellite 3 to achieve a further maximum reduction in the integrity risk. satellite 3 is therefore also added to the first subset. The satellites remain in the second subset 1 . 4 . 5 . 6 . 7 . 8th . 9 and 11 , whose information for determining the position of the terminal 20 be used. This is schematically in 7 shown.

in the embodiment Three iterations of the type described are performed. In the Practice can also more or less iteration steps are made.

It is assumed that the integrity risk that results from the use of the information of the satellites 1 . 4 . 5 . 6 . 7 . 8th . 9 and 11 is below a tolerable integrity risk. It will therefore be below for each of the satellites 1 . 4 . 5 . 6 . 7 . 8th . 9 and 11 Check if this is a critical satellite. In 8th are critical satellites shown with a bold, solid line. Again 8th It can be seen without further ado, the satellites represent 1 . 4 . 5 . 6 . 7 . 8th and 11 critical satellites while satellite 9 is a non-critical satellite. Critical satellite means that removing a critical satellite from the remaining second subset would increase the integrity risk of the remaining satellites beyond tolerable integrity risk.

In addition, it is checked whether the number of critical satellites is greater than a predetermined, maximum tolerated number of critical satellites. In the exemplary embodiment, it is assumed that the number of maximum tolerable critical satellites is six. This number may differ in practice from the selected value. How out 8th can be easily removed, the navigation system in the embodiment has a total of seven critical satellites.

It is therefore checked in the future, whether in the second subset and non-critical satellites are included. In the embodiment according to 8th sets satellite 9 This is therefore removed from the second subset and assigned to the first subset. It has been found that the described strategy can also influence the number of critical satellites. In the second subset, which will now be considered below, the satellites will initially remain 1 . 4 . 5 . 6 . 7 . 8th and 11 , Again, the integrity risk is determined and, for each of those satellites, whether it is a critical satellite. In the embodiment according to ge 9 is by removing the satellite 9 satellite 4 become an uncritical satellite. The satellites remain as critical satellites 1 . 5 . 6 . 7 . 8th and 11 ,

In the manner described now also the non-critical satellite 4 removed from the second subset and assigned to the first subset. In turn, it becomes the integrity risk for the remaining satellites 1 . 5 . 6 . 7 . 8th and 11 determined as well as whether the satellites are still critical satellites. In the exemplary embodiment, the number of critical satellites can be reduced by removing the uncritical satellite 4 do not further reduce, so that the second subset finally the satellites 1 . 5 . 6 . 7 . 8th and 11 which are each critical satellites. However, since the number of critical satellites in the embodiment no longer exceeds the number of maximum allowed critical satellites, the availability of the navigation system is ensured. Furthermore, the integrity risk is below the tolerable integrity risk.

By the procedure according to the invention This has the availability of the navigation system in the whole increased.

11 shows an example of the invention of the underlying method in its course. In a step S1, a plurality of spacecraft is determined, of which information about a position determination is available. In a step S2, the integrity risk of the plurality of spacecraft is determined. This means that the integrity risk is determined for the number of spacecraft which can be used maximally for determining the position of the terminal. In step S3, the integrity risk is minimized by iteratively removing one or more spacecraft from the plurality of spacecraft. In a step S4, it is checked whether the determined integrity risk is less than a tolerable integrity risk. If this is not the case, then the optimization algorithm ends at this point. In the affirmative case, it is checked in a step S5 for each spacecraft of the second subset whether this is a critical spacecraft. If at least one non-critical spacecraft is contained in the second subset (step S6), this is removed from the second subset in a step S7. This takes place until no uncritical spacecraft is contained in the second subset. At this point, the optimization algorithm ends.

By a targeted selection of available satellites for determining the position of a terminal, the availability can be improve the global navigation system in a simple way.

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Claims (12)

A method for increasing the availability of a global navigation system that supports multiple spacecraft ( 1 . 2 , ..., 11 ) for determining the position of a terminal ( 20 ) each information to the terminal ( 20 ), in which - of a majority of spacecraft ( 1 . 2 , ..., 11 ) each information to the terminal ( 20 ) be transmitted; - from the majority of spacecraft ( 1 . 2 , ..., 11 ) a first subset with at least a first spacecraft and a second subset with second spacecraft ( 1 . 2 , ..., 11 ), the second subset of the spacecraft ( 1 . 2 , ..., 11 ) is the difference between the majority of spacecraft ( 1 . 2 , ..., 11 ) and the first subset of spacecraft ( 1 . 2 , ..., 11 ) certainly; and - exclusively from those of the second spacecraft ( 1 . 2 , ..., 11 information integrity risk is determined, the first and second subsets of the spacecraft ( 1 . 2 , ..., 11 ) are determined such that the integrity risk arising from, from the second spacecraft ( 1 . 2 , ..., 11 information is compared with the integrity risk derived from the information of all spacecraft ( 1 . 2 , ..., 11 ) of the plurality of spacecraft ( 1 . 2 , ..., 11 ) is optimized. Method according to Claim 1, in which only the information of the second subset of spacecraft ( 1 . 2 , ..., 11 ) for determining the position of the terminal ( 20 ) be used. Method according to Claim 1 or 2, in which the information of the first subset of spacecraft ( 1 . 2 , ..., 11 ) not for determining the position of the terminal ( 20 ) be used. Method according to one of the preceding claims, in which the first subset and the second subset of spacecraft ( 1 . 2 , ..., 11 ) are determined iteratively, so that the integrity risk arising from, from the second spacecraft ( 1 . 2 , ..., 11 information is compared with the integrity risk derived from the information of all spacecraft ( 1 . 2 , ..., 11 ) of the plurality of spacecraft ( 1 . 2 , ..., 11 ) is minimized. Method according to Claim 4, in which, in order to minimize the integrity risk a), a number of spacecraft ( 1 . 2 , ..., 11 ) from the majority of spacecraft ( 1 . 2 , ..., 11 ) of the first subset and the integrity risk of the second spacecraft remaining in the second subset ( 1 . 2 , ..., 11 ) is determined; b) step a) is repeated for, in particular, all possible combinations of a first subset, c) those second spacecraft ( 1 . 2 , ..., 11 ) of the second subset, where the integrity risk is minimal, for a next iteration step the plurality of spacecraft ( 1 . 2 , ..., 11 ) form; d) the steps a) to c) are repeated until a minimum integrity risk is reached. Method according to one of the preceding claims, in which is being checked whether the integrity risk is lower as a tolerable integrity risk is. Method according to one of the preceding claims, in which for each of the second spacecraft ( 1 . 2 , ..., 11 ) of the second subset is checked whether this is a critical spacecraft. Method according to Claim 7, in which it is checked whether the number of critical spacecraft ( 1 . 2 , ..., 11 ) greater than a number of allowed critical spacecraft ( 1 . 2 , ..., 11 ). Method according to one of the preceding claims, in which, in order to minimize the number of critical spacecraft ( 1 . 2 , ..., 11 ) a) a non-critical spacecraft from the determined, in particular optimal, second subset of spacecraft ( 1 . 2 , ..., 11 ) is assigned to the first subset; b) the number of critical spacecraft ( 1 . 2 , ..., 11 ) is determined within the second subset; and c) steps a) and b) are repeated iteratively, until in the second subset no non-critical spacecraft ( 1 . 2 , ..., 11 ) are more determinable. Method according to Claim 9, in which the minimization of the number of critical spacecraft ( 1 . 2 , ..., 11 ) is performed when the number of critical satellites is greater than a maximum allowed number of critical satellites. Terminal ( 20 ) for determining a position using a global navigation system comprising a plurality of spacecraft ( 1 . 2 , ..., 11 ) for determining the position of the terminal ( 20 ) each information to the terminal ( 20 ), the terminal ( 20 ) Comprises means for carrying out the method according to one of claims 1 to 10. Computer program product that directly into the internal memory of a digital computer and includes software code sections, with which the steps are carried out according to one of claims 1 to 9, when the product is running on a computer.